March 29, 2012 – SLICE testing was completed on March
23 and the hardware has now been reconfigured for the Burning
and Suppression of Solids (BASS) experiment. After restoring
the video overlay, astronaut Don
Pettit conducted
SLICE tests twice per week for a seven-week period in February and
March. In the thirteen sessions (i.e., days) of testing, all
twelve bottles of gaseous fuel were consumed, during which approximately
120 flames were ignited and about 4,000 high-resolution photos were
taken at roughly 700 flow conditions. Preliminary estimates
have been made of flame liftoff limits for ten fuel and burner tube
combinations. With testing complete, the focus is on analyzing
the acquired data and using it to enhance the computational modeling
of the flames, extending our ability to accurately predict a broader
range of flame conditions. The improved modeling capability
will lead to design tools enabling improved fuel efficiency and reduced
pollutant emission in practical combustion on Earth. The analysis
and modeling activity is being led by Profs. Marshall Long and Mitchell
Smooke at Yale University as described in the online story, “Space
Station Research Comes Back to Earth.” To
view additional photos and learn more about the experiment, visit
the NASA/slice
Facebook page -
which is simply a web page and doesn’t require registration
with Facebook or special software.

Feb. 15, 2012 – When the hardware was set up by astronaut
Don Pettit on
Jan. 20, the video overlay was found to be stuck in a troubleshooting
mode (where it was scrolling hexadecimal characters)
instead of its normal mode where it displays the flow settings and
thermal (infrared)
radiation from the flame. This anomaly represented a major science
loss for SLICE and the subsequent BASS experiment. Furthermore,
the overlay could only be corrected with a set of switches which were not part
of the flight hardware. But the SLICE team developed a procedure
where temporary jumper (i.e., wire) connections were made to emulate
the switch action. This reset procedure was successfully conducted
by Pettit on
Feb. 6 and SLICE science subsequently began on Feb. 9. Between
two sessions on Feb. 9 (with 100% methane)
and Feb. 13 (with 40% methane), a total of 13 microgravity flames
have been ignited and data has been obtained for approximately 65
flow conditions. Two fuel bottles have been consumed and ten
more remain, where the next session is planned for Feb. 17. To
see photos and follow the experiment’s progress, you are very
strongly encouraged to visit the NASA/slice Facebook
page -
which is simply a web page and doesn’t require registration
with Facebook or special software.

January 18, 2012 – On the ISS,
astronaut Don Pettit is scheduled to unstow and set up the SLICE experiment
on Jan. 19 and 20, respectively. Testing is expected to begin
on Jan. 31 and be conducted twice per week in eleven sessions over
a period of 5.5 weeks. For more information about the SLICE
status, see the experiment’s Facebook
page.
December 2011 – The SLICE team in Cleveland has been busy
preparing for the experiment’s start with planning, practice
in the lab, and training activities including participation in a Multilateral
Joint Multi-Segment Training (JMST) simulation on December 8. As
planned, astronaut Don Pettit and fellow crew members launched from
Kazakhstan on December 21 and
arrived at
the space station on December 23, returning
the crew size to its normal six. You can learn more about Pettit
and his space
station activities
from his preflight
interviewand
Letters to Earth blog. You
can also follow what’s happening through the daily reports of
the crew
activities. The
MSG glovebox failed to power up on December 19, but this was corrected
with hardware replacement on December 28. With this short delay,
set up of the SLICE experiment is now planned for January 20.

November 2011 – While the MSG glovebox is currently being
used for the Selectable Optical Diagnostics Instrument (SODI), it
is expected that those tests will be completed in time for SLICE to
begin in mid January 2012. Astronauts Ron Garan and Mike Fossum
have both returned to Earth (in September and November, respectively)
so SLICE is waiting for the launch of astronaut Don Pettit which is
planned for December 21. Unless there is an unexpected delay,
Pettit will conduct the SLICE experiment. This is his second
time as an ISS crew member; Dr. Pettit previously served as Expedition
6’s Science
Officer and may be best known for his Saturday
Morning Science .

October
2011 – The Capillary Channel Flow
(CCF) experiment has been completed and the Microgravity Science Glovebox
(MSG) is now being used for investigations using the Selectable
Optical Diagnostics Instrument (SODI). SLICE operations will
follow both SODI and the launch of astronaut Don Pettit and are
still expected to occur in January-February 2012 (during Increment
30).

September 2011 – SLICE operations are approaching, and
will follow (in order) the CCF, SODI-Colloid,
and SODI-DSC experiments in the Microgravity Science Glovebox (MSG). It
is currently anticipated that SLICE will begin in January 2012, in
which case the experiment will be conducted by astronaut Don
Pettit. Final
SLICE operations (tentatively in February 2012) will include some
tests for the Smoke Point In Coflow Experiment (SPICE).

July 2011 - The SLICE
hardware launched in February 2011 on STS-133/ULF-5 and is currently
on board the International Space Station (ISS). Astronauts
Joe Acaba, Mike Fossum, Ron Garan, Don Pettit, and Suni Williams
have been trained for the experiment. Although Garan and Fossum
are both now on the ISS, the facility in which SLICE will be conducted,
i.e., the Microgravity Science Glovebox (MSG), is being used for
other experiments. It is currently expected that SLICE
operations will begin in early 2012 (or perhaps late 2011) where
that timing will determine which astronaut(s) conduct the experiment. SLICE
operations should last approximately two months, after which the
MSG will be used for the Burning
And Suppression of Solids (BASS) experiment.

Coflow laminar diffusion flames are especially valuable
for studies of combustion because of the availability of accurate
numerical modeling with that flame configuration. In particular, excellent agreement can be achieved
when the flow conditions are such that the flame detaches and lifts
above (i.e., moves downstream of) the nozzle. A coupled experimental
and numerical investigation can enable validation and improvements
to combustion modeling. For example, the image to the right is not
a photo, but a numerical simulation of a 40% ethylene flame. Enhanced
modeling capability is important because it can reduce time and cost
in the design of practical combustion devices. Furthermore,
flame attachment to (or detachment from) a burner or condensed-fuel
surface is of essential importance in both combustion systems and
fire safety. The flame attachment point controls the stability
of the entire trailing diffusion flame.

The SPICE hardware, used for SLICE, in the Microgravity
Science Glovebox (MSG) on the International Space Station.

Microgravity
testing allows for greater temporal and spatial scales and a broader
range of flame characteristics than can be achieved in normal gravity. As
one example of the NASA-recognized value of such studies, the Coflow
Laminar Diffusion Flame (CLD Flame) experiment of Marshall B. Long
and Mitchell D. Smooke (both of Yale U.) is currently in development
for conduct in the Combustion Integrated Rack (CIR) on the International
Space Station, as part of the Advanced Combustion via Microgravity
Experiments (ACME) project.

The overall goal of the proposed study is to improve
our understanding of the physical and chemical processes controlling
diffusion (i.e., non-premixed) flame structure and lifting phenomena
(i.e., stabilization) and to provide for rigorous testing of numerical
models, including thermal radiation, soot formation, and detailed
chemical kinetics. As part of this aim, an important purpose
of the SLICE investigation is to conduct preliminary microgravity
studies that will maximize the scientific return of the subsequent
CLD Flame experiment and mitigate associated risks. In other
words, SLICE is a precursor to the CLD Flame experiment.

Objectives

For diffusion flames of methane, ethylene, and selected
nitrogen dilutions of each fuel burning in a coflow of air:

(1) Characterize the structure of the flame, especially its base (i.e., stabilizing
region), from attached through lifted conditions as a function of the fuel, burner
diameter, and flow conditions.

(2) Identify the liftoff velocity limits as a function of the fuel and burner
diameter.

Approach

Flame liftoff was previously studied in a glovebox on the
space shuttle, with the Enclosed Laminar Flames (ELF) investigation
which flew as part of the STS-87 mission. The SLICE
experiment uses SPICE hardware which was based directly on
the earlier ELF hardware. Compared to ELF, the SLICE
experiment provides superior imaging and a much wider variety
of test conditions.

The
experimental hardware for the Smoke Points In Co-flow Experiment (SPICE),
of David L. Urban (NASA Glenn) and Peter B. Sunderland (U. Maryland),
which is currently onboard the International Space Station, was built
to allow studies of coflow laminar diffusion flames. The SPICE
hardware is within the ISS MSG in the image to the right. While
the SPICE investigation has been specifically focused on a study of
soot production and oxidation within flames, the hardware can be used
without modification to conduct the SLICE experiment. In terms
of the experimental hardware, the only additional requirements for
SLICE are more fuel (i.e., gas bottles), recording media, and minor
hardware elements such as new nozzle(s). The three existing
SPICE nozzles are all smaller than the nozzle planned for the CLD
Flame experiment. Of course, the SLICE testing could most benefit
the CLD Flame experiment by bracketing and/or including the same nozzle
size. It is also possible that screen(s) would be flown to alter
the velocity profile of the coflow.

The SLICE operating procedures will have some differences
to the standard SPICE procedures given the differing objectives. However,
those changes are fully within the capabilities of the SPICE hardware,
as demonstrated by exploratory testing that has already been conducted
on orbit. As a simple example, the standard SPICE procedure
calls for a fixed air velocity and an increase of the fuel flow until
the smoke point is reached. In contrast, SLICE will include
testing where the fuel flow is fixed and the air velocity is incrementally
increased until the diffusion flame detaches and lifts off from the
nozzle. In all cases, still and video measurements of the flame
structure will be made for comparison with detailed numerical computations. Given
that the capture of the lifting processes in normal gravity is extremely
difficult, SLICE will provide valuable photographic observations on
the transient flame behavior.

The lifted nature of the flames can be discerned from the flame
shape in the example images (which are not at the same scale) and
the distance from the nozzle tip (which is not visible). While the
case(s) on the left may look similar to attached flames, the outward
fuel-lean flare of each flame’s base reveals it’s lifted
nature.

Example of preliminary SLICE results prepared by
the project team at Yale University, under the leadership of Prof.
Marshall Long. It shows an attached flame of 100% methane from a
test conducted on Feb. 9, where it was photographed through a blue-green
(BG7) filter to prevent saturation in the red from the bright soot.
Hydrocarbon flames are naturally blue (because of the chemistry,
i.e., chemiluminescent emission of excited species, especially CH*),
whereas the yellow, orange, and red coloring is from broadband radiation
from the hot soot particles. The flame color was then reconstructed
and preliminary estimates were made of the soot concentration and
the soot temperature. The temperature was determined by a
color-ratio process using the individual RGB (red/green/blue) planes
of the digital still photo, based on a blackbody calibration of
the camera conducted prior to its launch.

Measured and computed temperature profiles of coflow laminar diffusion
flames of 65% methane and 35% nitrogen in both normal gravity and
microgravity. See large
image for a side-by-side comparison. (Yale
University)